In the maintenance of railroads, the crossties of a rail bed are cut to form grooves or seats in the ties for the reception of rail chairs, which support the rails. Adzing tools are used to cut the railroad crossties. For example, one or more adzer heads are rotated about a vertical axis and moved along a railroad track to progressively cut the upper surfaces of the railroad crossties for the placement of rails along the crossties. Each adzer head includes a plurality of adzer bits, which are rotated by the adzer head in an orbit about the vertical axis. The adzer bits each include an annular cutting structure that is typically formed of hardened metal that cuts into the crossties. In order that the cutting bits last for a long time, it is desirable that they be fabricated of very hard material; however, the very hard materials are brittle and are subject to chipping and cracking during use. Portions of the annular cutting structure are protected by a shield member, which is typically made of a softer material than the cutting structure. During use, the shield member wears away to progressively expose the cutting edge of the annular cutting structure.
U.S. Pat. No. 4,506,715 to Blackwell entitled “Adzing Bit Assembly” is hereby incorporated by reference and discloses a conventional adzer bit with a unitary annular cutting structure. Portions of the '715 Patent are briefly shown and described below as an example of conventional adzer head assembly.
Reference is made to FIG. 1, which illustrates a conventional adzer head 10 supporting a plurality of adzer bit assemblies 25 about its periphery. The adzer head 10 includes a central opening 11 that is coaxial with the center 12 of the adzer head 10 and a circular array of smaller openings 13 which are circumferentially spaced about the adzer head 10. The central opening 11 is shaped to fit over a hub of a fly wheel or other rotary drive means, (not shown) while the openings 13 are adapted to be aligned with similar openings of the flywheel and to receive connecting screws. The adzer head 10 is rotated in the direction of arrow 16 about a vertical axis which is coaxial with the center 12 of the adzer head 10. A plurality of bit support portions 15 are disposed radially from a central portion of the adzer head 10. The bit support portions 15 are equally spaced apart from each other circumferentially. The bit support portions 15 provide opposed parallel mounting surfaces 18 and 19, with the leading surface 18 of each bit support portion 15 formed in a plane that extends through the center 12 of the adzer head 10. A cylindrical bore 20 through each bit support portion 15 is oriented in a plane perpendicular to the axis of rotation of the adzer head 10 and perpendicular to the opposed parallel mounting surfaces 18 and 19.
With reference to both FIGS. 1 and 2, an adzer bit assembly 25 includes a shield 26, an annular cutting structure 27, a support member or bushing 28 and a connector bolt 29. The shield 26 protects the annular cutting structure 27 and defines a central cylindrical through hole 33. Annular cutting structure 27 includes opposed parallel first and second support or bearing surfaces 40 and 41, peripheral surface 42, and central cylindrical through hole 43.
The support member or bushing 28 also includes a central cylindrical through hole 53. A first large diameter hub 54 extends toward the trailing mounting surface 19, and a second smaller diameter hub 55 protrudes from the large diameter hub 54, with the hubs 54 and 55 being coaxial with respect to the support member 28. The facing surfaces of the annular cutting structure 27 and of the support member 28 are silver soldered together.
The central cylindrical opening 33 of the shield 26 is fitted about the smaller diameter hub 54 so that it is in facing relationship with respect to the annular cutting structure 27. The cylindrical opening 33 is press-fit about the smaller diameter hub 54 of the support member 28. The connector bolt 29 is then inserted through the bore 20 of a bit support 15 of the adzer head 10, and the nut 62 is threaded onto the protruding threaded end portion 61 of the bolt 29. A washer 65 is positioned between the nut 62 and the mounting surface 18 of the bit support portion of the adzer head 10.
The annular cutting structure is typically formed of an ultra-hard material and is therefore brittle and subject to cracking during use. A crack that initiates in one portion of the annular cutting structure 27 may propagate to other portions of the annular cutting structure 27 and thereby reduce the structural integrity of the annular cutting structure 27 such that it breaks away or otherwise is no longer an efficient cutter and must be replaced. Frequent replacement of adzer bits is inefficient and costly.